Among the governor's primary challengers, Republican Neel Kashkari already has invested $2 million of his own cash in a bid for the governor’s office. Earlier this week, Kashkari said he wouldn’t rule out tapping into his personal bank account in the future.

The most recent campaign finance reports were not available for Kashkari, a former U.S. Treasury official, or his main GOP rival in the race for the gubernatorial nomination, Assemblyman Tim Donnelly of Twin Peaks.

Thursday is the deadline for all candidates to file their latest campaign finance reports to the California Secretary of State.

California's primary election is Tuesday, June 3.

The two candidates in the governor's race who receive the most votes will face-off in the November general election.